Biosorption kinetics and isotherm studies of Acid Red 57 by dried Cephalosporium aphidicola cells from aqueous solutions

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Abstract

Equilibrium, kinetics and thermodynamic studies on the removal of Acid Red 57 (AR57) by biosorption onto dried Cephalosporium aphidicola (C. aphidicola) cells have been investigated in a batch system with respect to pH, contact time and temperature. The results showed that the equilibrium time was attained within 40 min and the maximum biosorption capacity of AR57 dye onto C. aphidicola cells was 2.08 × 10−4 mol g−1 or 109.41 mg g−1 obtained after contact with 0.4 g dm−3 biosorbent concentration, pH0 of 1 and at a temperature of 20 °C. The pseudo-second-order kinetic model was observed to provide the best correlation of the experimental data among the kinetic models studied. Biosorption isotherm models were developed and the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were conformed well to the experimental data. The changes of free energy, enthalpy and entropy of biosorption were also evaluated for the biosorption of AR57 dye onto C. aphidicola cells.

Introduction

Dyes are extensively used in paper, textile, dyehouses and printing to colour the final products [1]. They usually have a synthetic origin and complex aromatic structures making them more stable to be degraded [2] and are classified as anionic, cationic and nonionic dyes [3]. Their discharge into natural waters causes several problems because they can be toxic to the aquatic life by reducing light penetration, are carcinogenic and mutagenic [4]. Moreover, they affect severely to human beings by damaging the liver, the kidneys, brain, central nervous and reproductive systems [5].

Dye containing effluents from textile and dyestuff industries are the most difficult to treat and present unique problems as they show resistance to many chemicals, oxidizing agents, light and heat and are biologically nondegradable [6]. Existing coloured wastewater treatment methods involve in a combination of physical and chemical processes including precipitation, sedimentation, ultrafiltration, reverse osmosis, flotation, colour irradiation, oxidation, ozonation and coagulation. However the use of above mentioned technologies in the colour removal from dye effluents are restricted due to technical and economical reasons ranging from little applicability to a wide range of dye wastewaters to high operating costs [7], [8].

Adsorption has appeared as an effective alternative process for optimising colour removal from dye contaminated solutions. The most popular and widely used adsorbent material is activated carbon which has high adsorption capacity, surface area and degree of surface reactivity as well as microporous structures [9], but it shows disadvantages of high operating costs and problems with regeneration [10]. This led to a search directed at developing low cost and locally available adsorbing materials with maximum adsorption capacity. Microbiological methods like biosorption have found utility in this context and applied not only to the biosorption of organic effluents such as methylene blue dye [11] but also to the recovery or removal of heavy metal ions such as lead, chromium and gold from industrial effluents [12], [13].

The purpose of this study was to investigate the biosorption properties of AR57 dye by dried cells of a filamentous fungus, C. aphidicola used for microbial hydroxylation of various substrates including monoterpenes [14], diterpenoids [15], [16], sesquiterpenes [17] and steroids [18], [19], [20]. The information about the biosorption of dyes from aqueous solutions onto C. aphidicola has not found in the literature so far. The dynamic biosorption behaviour was examined on the effect of equilibrium time, pH0, dye concentration and temperature. The kinetics and isotherm studies of biosorption of AR57 were investigated using various kinetic and isotherm models and the thermodynamic parameters were also deduced.

Section snippets

Microorganism, growth conditions and biosorbent preparation

The filamentous fungus, C. aphidicola IMI 68689, was obtained from Prof. James R. Hanson at Chemistry Department of Sussex University, Brighton, England. Media [21] and liquid growth conditions for C. aphidicola were described in our previous studies [22] while the biosorbent was prepared as follows: the live C. aphidicola cells were filtered after 7 days of growth, spread on petri dishes and dried in an oven at 60 °C overnight. They were then powdered using a mortar and pestle and sieved to

Effect of pH

Fig. 1 shows the effect of solution pH0 on the biosorption of AR57 onto dried C. aphidicola cells. As shown in this figure, the equilibrium biosorption capacity of the biosorbent decreased proportionally with increasing solution pH0 between 1 and 5 after which it reaches the lowest level of zero biosorption capacity at pH 6. The maximum biosorption capacity of the biosorbent was observed as 74.38 mg g−1 at pH0 1. This finding indicates that a significantly high electrostatic attraction exists

Conclusions

In this research the biosorption behavior of AR57 dye onto C. aphidicola cells has been investigated with variations in parameters of pH0 and contact time at different temperatures. The experimental data were evaluated by Langmuir, Freundlich and Dubinin–Radushkevich isotherms and fitted well to the all of the isotherm equations. Biosorption of AR57 dye onto C. aphidicola cells obeys the pseudo-second-order kinetic model and it also follows intraparticle diffusion model up to 40 min. It was

Acknowledgement

The authors thank Prof. James R. Hanson at Sussex University, England for kindly providing C. aphidicola.

References (37)

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